In the Battle of Kleidon there is the mass blinding of Bulgarians, I always have heard that rebels and such were likewise mutilated. It may be confirmation bias, but I feel as though it's more common than many other places.
Mutilations during the heyday of the Byzantine empire was pretty common, particularly among royals. This was more of a thing in the early stages of the empire (roughly 600 AD - 1000 AD), and the people who were often mutilated were deposed emperors or rivals for the throne.
The reason for that is because the Byzantines believed that someone who had a physical imperfection could never be an emperor. As a result, when an emperor was overthrown, it was common to blind them, cut off their ears, nose, or tongue, and by doing so, effectively remove any chance that they'd come back to power.
Of course, over the years, there were blinded/mutilated rulers of Byzantium, so the practice lost its potency over time, but never really quite went away while the Byzantine Empire was alive.
Source: Short History of Byzantium, by John Julius Norwich. It's a great introductory single-volume work, and Norwich is very readable. He also did a 3 book series (which the single volume work is adapted from), if you want a slightly more in-depth read.
Edit: Slight edit to the years during which mutilations occurred - thanks to shlin28 for the heads up.